In a conventional induction motor, when the motor is subjected to load, certain undesirable effects occur. More specifically, when current flows through the rotor conductors, a rotor reaction is produced in the air gap which changes both the magnitude and distribution of the flux crossing the air gap and adds vectorially to the main magnetic field flux, producing a resultant magnetic field flux which lies in a different direction from the main magnetic field flux, causing phase and wave form distortions.
Another undesirable effect is the production of high frequency flux in the air gap, causing losses, heating and dielectric breakdown.
In studying these problems of the conventional motor, we have found that the rotor reaction and high frequency flux in the air gap can be greatly reduced by providing a double set of closed loop ring coils in combination with nonmagnetic material in the rotor without necessitating substantial changes in existing equipment and in normal techniques of winding and installation of such a winding.